Options that trick you into installing potentially unwanted programs are common during the setup of free tools and programs. Here's how to spot them and keep them off your system.

They're called PUPs—Potentially Unwanted Programs—and they sneak onto your system as accessories to the program you actually intend to install. They're annoying, and they can result in slower performance, space-stealing browser toolbars, annoying pop-ups, and even loss of privacy.

You don’t have to give up free software to avoid PUPs, but you do have to pay attention. Each PUP first appears as a trap in the desired program’s installation wizard.

Ian Paul recently recommended a program called Unchecky that attempts to uncheck installation options for you, but I prefer just being careful. Here are some tricks and traps to look out for during software installations.

Not too long ago, I needed a simple program that could do one simple task: Convert a video DVD—a DVD I created myself, with no DRM issues—into an ISO file. So I downloaded FreeAudioVideoSoft’s All Free ISO Ripper.

As I walked through the installation wizard, I found something of a PUP mother lode. Every dirty trick I knew, and a few I hadn’t seen before, popped up during the installation. This made the ISO ripper a perfect tool for teaching people how to install a program…and only install the program.

I tend not to trust supposed Windows “optimizers.” In almost every case, the software is either too cautious to do any good, or too reckless to be safe. Obviously, I would want to uncheck the option to install PC Utilities Pro: Optimizer Pro.

Except, there’s no such option to uncheck.

You can uncheck I accept the Optimizer Pro Terms of Use and Privacy Policy, though. If you don’t want to install a program, you don’t have to accept its Terms of Use or Privacy Policy—even if it’s on by default…and appears to be grayed out.

Finally! Something we all know and ignore: the program's End User License Agreement. There's nothing like a massive block of dense legalese to make you select Accept and go on with your life.

But before you do so, take a second look at this particular EULA. The title reads "All Free ISO Ripper includes RelevantKnowledge." The first sentence also mentions RelevantKnowledge as software "included in this download."

The real relevant knowledge, so to speak, is that this isn't the All Free ISO Ripper EULA.